I use GWX, and recommend it heartily. It is such an amazing difference to the game I hesitate to tell anyone to run stock SH3, except that you'll never realize how good GWX is if you don't!
Even with any of the mods, though, there is no improving the ship/convoy AI.
It is still entirely possible, early in the war while merchants are unarmed, to take down 2-3 or even 4 escorts and then use your deck gun and remaining torpedoes to lay waste to entire convoys. In real life they would scatter or try to ram. There is no ramming behavior from merchants that I can tell.
As was noted, with GWX the days of being able to engage in gun duels with escorts are over. I
have done it against a trawler once and won, but took a lot of damage in the process.
Welcome aboard!
Steve